Even a 2% cuckold rate is rather disconcerting, given the enormous emotional and financial costs in raising a child (uncountable for the former, and hundreds of thousands of dollars [at least] for the latter). On top of which, in the US at least, a cuckold father can be held responsible for the care of someone else's child even if he does learn of the matter.

From a game theory perspective, if you assume that it costs $250,000 to raise a child, then your expected loss due to cuckoldry is about $5000, which is more expensive than a $200 DNA test.

"For if people in the past were as adulterous as the data suggest those now alive are, how did they conceive so few children doing it?"
The Author fails to consider the significantly larger proportion of infant deaths and abandoned babies back in the 17th Century.

Put it this way: infant mortality rates are equal for both "legitimate" children and "extra-pair paternity" children. Therefore, both are equally likely to die.

Their relative proportions should therefore not be affected significantly by infant mortality.

Unless you can find a compelling reason and evidence that "extra-pair paternity" children are more likely to suffer from infant mortality (e.g. because suspicious fathers neglect them more), then I don't see this is as much a factor as you might think.

Good god, do they let anyone wander in off the net onto Economist forums? I'd like to think that paying for a subscription would be adequate to filter out the epsilons but it looks like they'll need to adopt more effective measures.

Sorry for the pomposity but seriously! I come here to read and exchange ideas from my peers across the globe not to read that someone cannot differentiate reproduction and immigration.

Please look back farther in The Economist archives. I remember an article from 10+ years ago about a study of the paternity of children in a British town, and the conclusion that the EPP rate (somewhere in the range of 12 - 15%) was quite similar to that of certain "monogamous" birds.

Actually it is the 15% EPP number that have always been suspect. I tried to track them down and the source always banishes or is quoted back to a single off-the-record comment made by an organ donor surgeon.

For example, in Britain the press usually trudges out a 30% EPP number. When one searches this turns out to be the number of EPP cases among people who already had strong reason to believe the kid wasn't theirs e.g. the mother admitted to having an affair around the time of conception.

Well, for a start, the withdrawal method is far, far more effective than sex education would have young people (at least when I had my sex ed in the UK during the 90s and early 00s) believe.
Combined with fluctuations in female ability to conceive, and limits placed on the number of times that (most) adulterers will have sex, that surely accounts for a great number of non-babies.

It doesn't in terms of pure statistics, but it provides a much larger forest in which to hide a tree of infanticide (killing of babies from adultery by the mothers). Similarly, larger pool of abondoned babies would provide cover for abandoning of babies from adulterous relationships (as was practiced by the mother of Moses).

I came here to mention the same thing. That article--some 15 years ago about a study in Bristol reporting a 10% EPP (if I remember correctly) and discussing paternal resemblance--was what opened my eyes to the subject of Evolutionary Psychology. Since then I have noted that people without fail will comment on a child's resemblance of its father. I believe that Matt Ridley, author of The Red Queen, was then editor of the Science & Technology section.

If last weeks "How Science Goes Wrong" helps to spur calls for repeat studies to validate data, and encourages all centers to voice the call to get science research back on track, that will be a great correction to the trend of last decades.

Of course, there is the possibility that many of the extra partners were close relatives of the male partner. In that case, the tests do not capture true paternity. Thus, these numbers may be understatements.

As a quick-and-dirty acid test I can think of an incident that happened to me. More broadly, I can think of how incredibly often people comment on paternal resemblance. They could say anything about a child, but more than half the time their first comment is about paternal resemblance. An important instinct seems to be operating here.

But is paternal resemblance really usually strong enough to fully confirm or discount paternity? It is usually fuzzy enough that there is room to doubt or believe, depending on one's inclinations.

Anyway, I just wish The Economist would acknowledge its own previous article on the subject.

In the recent past marriage determined paternity in that a man was legally responsible for children born to the woman to whom he was legally married. This is no longer the case, in that a man is not liable for child support (in the event of a divorce) if a genetic test determines he is not the biological father. However, a man who was not the father of his wife's child was not necessarily a cuckhold. A great aunt of mine was impregnated by a man of the household in which she worked as a maid, but married by another who accepted this situation. A childless woman might go outside her marriage with tacit consent, inasmuch as the household was a unit of production dependent on children's labor.
On the other hand, this study would be unable to detect a woman's extramarital pregnancy if she selected her husband's father, brother,FBS, etc. And these might be the males most available in the vicinty. One may conclude that women were either quite faithful or engaged only in well-thought-out premeditated infidelity or both.